Hudyma, Nick¹, Zoe K. Shipton² 
(1) University of North Florida, Jacksonville, FL 
(2) Trinity College, Dublin, Ireland

ABSTRACT: Comparison of Laboratory and Geologically Produced Clay Smears

Layered sand and clay specimens have been deformed using a novel apparatus that allows the user to visually monitor the evolution of the deformation. Four specimen sets with different layering geometries were used. Each specimen developed a series of preliminary structures before forming a clay smear. Offsets less than the layer thickness produced deformation bands in the sand layers and slip lines in the clay layers. As the offset increased, steps formed between non-coplanar structures. Finally through-going clay smears developed. As deformation continued, pockets of relatively undeformed sand formed within a zone of anastomosing clay bands. The displacement at which each of these structures formed was a function of layering geometry. 
The laboratory specimens were compared to field examples from southeastern Utah, which have offsets ranging between cm’s to km’s. Similar structures, such as step structures and sand pockets, occur at a variety of scales. Structures that were not found in the laboratory smears, such as pinching and disconnection of clay layers in the fault zone, may be due to the density (packing) of the sand and/or the consolidation state of the clay within the laboratory specimens and/or increased offset. The similarity between structures produced during laboratory deformation and the field examples suggests that they may have evolved through similar intermediate stages of deformation. Correlating force and displacement measurements with the geometrical evolution of clay smears in the laboratory will help in understanding the processes of clay smear development and assist in the calibration of clay smear fault seal algorithms.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.